In oil well drilling and completion operations, drill strings are used. These drill strings often comprise various types and sized of tubular components like drill pipes, drill collars, liner, casing, and tubing in various configurations. In coupling such tubular ends, sometimes functionality is required, such as rotatablity of one end with respect to an adjacent end.
In U.S. Pat. No. 5,074,681 a thrust bearing assembly is described in the form of a spring assembly reaching in an annular space between a housing tube end and a drive shaft. The spring assembly is provided with bearing means whereby first race members are secured within the housing tube end. The second race members transmit the load to axially spaced apart spacer rings which are rotatable with the drive shaft and are kept in their spaced apart positions by a series of sleeve members. The load is axially transmitted through the series of spacer rings and sleeve members. The last spacer ring is axially supported by the drive shaft by means of a shoulder, so that an axial load can be transmitted from the drive shaft to the series of spacer rings and sleeve members.
It is an object of the invention to provide an improved system for coupling two tubular ends for use in a bore hole, such as a well bore.
In accordance with the invention, there is provided a system for use in a bore hole, such as a well bore, for axially coupling a tubular end with a mandrel, the system comprising a tubular end, a mandrel for inserting into the tubular end in axial alignment thereof, thereby forming an annular space between the tubular end and the mandrel, and a connecting assembly that at least partly reaches in the annular space and that comprises two or more transmission units each being arranged for axially coupling the tubular end with the mandrel, wherein the transmission units each comprise a first fixture element, a second fixture element, and spacer means for maintaining an axial displacement between the first fixture element and the second fixture element, whereby the first fixture element is axially connectable to an inner surface of the tubular end and the second fixture element is axially connectable with the mandrel.
Each transmission unit itself is arranged for axially coupling the tubular end with the mandrel. This has the advantage that the full load is divided over two or more coupling points on the tubular end and the mandrel. At the same time, these transmission units may either act individually or in concert with other transmission units. Thus both coupling and the other functionality can be independently optimised and mounted.
By providing the spacer means additional to the fixture elements, the coupling functionality is separated from other functionality attributable in the connecting assembly.
The provision of a separate connecting assembly between the tubular ends, allows for adding additional functionality to the system. This functionality can conveniently be provided by a selection of a customized connecting assembly, and therefore the system is easily adaptable to custom need. Due to its at least partial reach into the annular space, the connecting assembly is protected from the outside by the tubular ends themselves that are connected by the connecting assembly.
The two or more transmission units may be interconnected so as to form a string of interconnected transmission units.
For instance, the connecting assembly, and in particular the spacer means, may be provided with one or more of the following features.
The spacer means may comprise adjustment means for adjusting the axial displacement. Herewith it is achieved that the fixture elements can for instance be coupled to their respective tubular ends at an approximated position and the axial displacement can subsequently be altered in a more controlled way without having to uncouple one or both of the fixture elements. In an embodiment, the adjustment means comprises a thread connection defining a thread path essentially coaxial to the mandrel.
In an embodiment of the invention, the spacer means comprises a bearing element cooperating with a bearing race supporting the bearing element in a plane perpendicular to the alignment axis, whereby the first fixture element is rotatable with respect to the second fixture element about the alignment axis.
In an embodiment, the spacer means comprises resilient means for providing axial resilience to the tubular ends when coupled. Also, the resilient means help to distribute the axial load proportionally over each available transmission unit.
Preferably, the resilient means in at least one of the transmission units has a lower stiffness than the resilient means in another one of the transmission units. By varying the stiffness of the various transmission units, the distribution of the load over the transmission units can be influenced. A lower stiffness leads to a lower portion of the load being transmitted via that transmission unit.
In an embodiment, the system further comprises first locking means for establishing a releasable axial coupling between the first fixture element and an inner surface of the tubular end. Herewith it is achieved that the tubular end can be conveniently released and slided from the connecting assembly so that the connecting assembly becomes exposed, for instance for maintenance. Or, during assembly, the mandrel with the connecting assembly already mounted on it, can be inserted into the tubular end and a releasable axial coupling between the first fixture element and the inner surface of the tubular end can then be established.
The first locking means may for instance comprise an opening provided through a sidewall of the tubular end, a receiving opening in the first fixture element, and an insertable locking member for extending through the opening and reaching in the receiving opening when in axially locked condition. This is locked by bringing the receiving opening in the first fixture element into alignment with the opening in the sidewall of the tubular end and inserting the insertable locking member.
In an embodiment, the system further comprises second locking means for axially releasably locking the second fixture element on an outer surface of the mandrel. This locking means may for instance be controllably lockable and releasable by a relative rotation of the second fixture element the mandrel about the alignment axis.
Preferably, the second fixture element is shaped to embrace the locking portion of the mandrel over essentially its full circumference. Herewith an even distribution of the axial force between the tubular end and the mandrel over the locking portion is achieved. Also, this geometry is advantageous for centring other features of the connecting assembly around the mandrel.
In an embodiment, the second locking means comprises at least one couple of cooperating locking rim segments, one locking rim segment of which couple being provided on the locking portion of the mandrel and one locking rim segment of which couple being provided on the second fixture element. By bringing the couple of cooperating locking rim segments in axial alignment, the second fixture element is locked to the mandrel such as to transfer axial force from one to the other. By relative rotation around the alignment axis, the segments can be brought to axial misalignment, in which position the second fixture element is no longer locked. Herewith the second fixture element is quickly mountable to and/or dismountable from the mandrel.
Means may be provided to secure the second fixture element and the mandrel in alignment to prevent them from inadvertently coming in axial misalignment.
In addition to the couple of cooperating locking rim segments, an additional locking rim segment can be provided on either the tubular element or the mandrel, such that the locking rim segment on one tubular end is sandwiched between the cooperating locking rim segment and the additional locking rim segment on the other tubular end.
In the Figures like reference signs relate to like components.